Metal-ligand cooperativity across two sites of a square planar iron(ii) complex ligated by a tetradentate PNNP ligand.

An iron(ii) complex with a square planar geometry and S = 1 ground state was synthesized using a rigid tetradentate bisphosphine-bisamide [PNNP]2- ligand. This complex was shown to bind an equivalent of PMe3 to produce a five-coordinate low spin complex, and to react with two equivalents of borane reagents via addition of two B-H bonds across the metal-amide bonds in a metal-ligand cooperative fashion.